THE NEPHRIDIUM OF LUMBRICUS. 333 



Pig. 28. — The nephrostome of an Enchytrseid (modified from Michaelsen) 

 in surface view, to show the nephrostome formed by the terminal per- 

 forated cell. 



Fig. 29. — A series of nephridial funnels in optical section, diagrammatically 

 represented to exhibit the possible evolution of that of Lumbricus and 

 others («?) from that of an Enchytraeid («). The intermediate form (b) is met 

 with in Urochseta; that represented by c is, as far as I know, hypothetical. 

 Between a and b that of Per. malamaniensis may be inserted. 



Figs. 30—32. — Diagrammatic views of constituent cells of a nephridium. 

 Fig. 30. A perforated (drain-pipe) cell, as met with in the ampulla. 

 Fig. 31. A drain-pipe cell from the middle tube. 

 Fig. 31 «. The same in longitudinal section. 

 Fig. 32. A gutter-cell from the nephrostome of Lumbricus. 



Arenicola piscatorum. 



Fig. 33. — A complete nephridium. Surface view, under a low power. 

 The specimen was removed from the body, stained in borax carmine, and 

 mounted in Canada balsam. The natural size is shown by the line (n. s.) 

 underneath. The nephridium is seen from its ventral side, and the gonad, 

 which in life is closely connected with it, has not been drawn. The network 

 of blood-vessels, in black, is drawn as far as I could make it out ; no doubt 

 it is more complicated and extensive than is shown, a is a branch of the 

 branchial vessel, passing to the nephridium. a' is a branch to the gonad, 

 passing behind the nephridium. b is the other end of this (cut) after passing 

 through gonad to join the network in the nephridium. mes. is a small piece 

 of mesentery, which suspends the funnel to the ventro-lateral muscle. 



Fig. 34. — A portion of the network in the " neck " of the nephridium, 

 drawn under a higher power, and showing the csecal dilated terminations {di.). 

 The coelomic epithelium {ccel. ep.) is drawn in part of the figure. 



Fig. 35. — A longitudinal section through the body of the nephridium, with 

 the ovary in situ. The blood-vessel marked b is intermediate between a' 

 and b in Fig. 33. 



Fig. 36. — A section through the neck of the funnel, with a couple of ova 

 within. 



Fig. 37. — A section along the funnel and neck, with neighbouring parts of 

 the body-wall and ventro-lateral muscle {nms.). The letter p points to the 

 relative position of the nephridiopore, which occurs several sections further 

 back. 0. is an ovum. 



Fig. 38. — A portion of the epithelium on the edge of the ventral lip of 

 the funnel (from Fig. 36, under high power). 7i. Nucleus. 



Fig. 39. — A portion of the epithelium lining the ventral lip (under high 

 power), n. Nucleus. 



Fig. 40.— Similar section through dorsal lip. 



Fig. 41.— a portion of the lining epithelium of the body of the nephridium 



